This invention relates to respiratory apparatus and, in particular, to breathing circuits with capability for maintaining humidified status of aeriform substances therein in order to inhibit or to control formation of condensate from the substances.
Respiratory apparatus is familiar in medicine and surgery for ventilation and therapy of the lungs, administration of anesthetics and other medicaments, and other procedures. The breathing circuit of exemplary respiratory apparatus, such as a mechanical pulmonary ventilator, implements delivery and exchange of aeriform substances for and from the patient by way of inspiratory and expiratory channels. Each channel provides a flow path enclosed by wall portions of a conduit and of a patient interface which, commonly, is a shaped tubular wye piece. The conduit may be a flexile hose or hose-like article. The wye piece has an inspiratory airway as the delivery end of the inspiratory flow path, an expiratory airway as the beginning of the expiratory flow path, and a third airway common to the other two. The wye piece may be joined with an endotracheal tube, a tracheostomy tube, or a face mask on the patient.
The background for this invention includes these points:
(a) A pulmonary ventilator, as an exemplary respiratory device, has a breathing circuit and a humidifier. The humdifier is up-path of the breathing circuit and serves to raise the temperature of and add water vapor to aeriform substances destined for the patient.
(b) Aeriform substances in the breathing circuit are likely to sustain heat losses to walls of the circuit's conduits. The losses decrease the capacity of the substances to retain water vapor.
(c) The ventilator does not provide means downpath of the humidifier for increasing absolute volume of water vapor in aeriform substances in its breathing circuit.
Safe and effective operation of a breathing circuit requires proper humidification and heating of aeriform substances delivered by the circuit. If water vapor in the substances in a conduit of the circuit reaches saturation level as a result, for example, of heat losses noted in point (b), aqueous condensate is likely to form. This condensate is recognized as hazardous and potentially fatal because, as it pools or accumulates, it harbors infective agents, may be inhaled by the patient, and may obstruct or occlude the inspiratory conduit thus restricting delivery of the substances and imposing increased labor of breathing on the patient.
Various products and methods have been proposed to deal with unwanted effects and liabilities of such condensate. My U.S. Pat. Nos. 3,865,106 and 3,945,378, and other patents, relate to breathing circuits in which the inspiratory conduit, to reduce heat loss therefrom, is coaxial with and located within the expiratory conduit. My U.S. Pat. No. 4,333,451 teaches closed-system condensate removal from breathing circuits. U.S. Pat. No. 4,967,744, to James Chua, discloses a breathing circuit with a coaxial arrangement of conduits and an electrical heating wire on the inspiratory conduit. U.S. Pat. No. 5,357,948, to Heinz Eilentropp, which is hereby incorporated by reference, discloses heatable respiratory hose with a heating wire or conductor on the outside of the hose and a connection to an electric power supply. Some such devices, products and methods are in service.
Electrical heating wires immediately proximate flammable or combustion-supporting inhalants, or aqueous condensate, may have unwanted safety implications. A regulatory alert was issued in 1993 because of safety problems reported in connection with electrical heating wires in ventilator breathing circuits. Accordingly, need continues for means and methods safely to control relative humidity and to inhibit and control condensate formation in breathing circuits.